In the case of the pattern recognition, a calculation of similarity between data is a fundamental calculation. As a general association memory, the content addressable memory (hereinafter, denoted as CAM) is well-known. In the case of the general CAM, if input data are coincident with stored data, it is possible to retrieve the stored data with reference to the input data, but it is impossible to retrieve data which are similar to the input data.
PTL 1 discloses an association memory which calculates degrees of similarity in parallel by use of hardware to retrieve data which has the maximum degree of similarity.
The association memory described in PTL 1 includes a storage circuit which stores reference data, a comparison circuit which compares input data with the reference data, and a pulse generating circuit which generates a pulse corresponding to the comparison result outputted by the comparison circuit.